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how could bacteria survive the sheer energy involved in that initial impact? There's the famous story of the manhole cover in los alamos that was launched into

how could bacteria survive the sheer energy involved in that initial impact? There's the famous story of the manhole cover in los alamos that was launched into orbit by an underground nuclear test- but in reality that manhole cover was turned into aerosolized iron. Ablation from air friction is proportional to both speed and air pressure. For an explosion to launch terrestrial rocks into space, the speed would have been highest at the surface where pressure is the highest. Yes, some meteoroids survive to fall to the earth's surface- but they decelerate gradually, starting up where the atmosphere is thinnest. And even then those get heat-sterilized, don't they?

adrian_b 2y ago
If the bacteria were deep inside a rock ejected by an impact on a planet, which then falls as a meteorite on the other planet (as it is known to have happened for some meteorites fallen on Earth, which had been ejected from Mars or from Moon), then bacterial spores could survive, even if the external layers of the original rock are vaporized by the heat, if the rock had been big enough, so that the inner part would not have reached a high temperature. The same happens with the astronauts coming back to Earth, who survive despite the external shield being vaporized by the heat. If a body has low thermal conductivity and high thermal capacity, the inner part will maintain a low enough temperature, even when the outer part is above boiling temperature. On Earth, one can find bacteria in some rocks that are not completely compact, but which have pores or crevices, through which the water and gases needed by bacteria can pass. Such events would be unlikely, but not impossible. In the early Solar System, when big impacts were very frequent, there must have been many cases of rocks traveling between close planets, in all directions. After the planets had reached their current structure, meteorites coming from either Mars or Moon to Earth have remained frequent, due to the lack of a thick atmosphere on Mars and Moon, combined with their weaker gravity, but meteorites going from Earth to any of them have become extremely unlikely, because most bodies colliding with the Earth do not reach its surface, and for the few that reach the surface the probability that an ejected rock could exit Earth's atmosphere is even lower.
- knodi123 2y ago
  > and for the few that reach the surface the probability that an ejected rock could exit Earth's atmosphere is even lower. Ah, but the case I was replying to was about rocks making the trip back in the era when earth and mars both had enough atmosphere to support flowing liquid water.
pyinstallwoes 2y ago
Particles from Venus reach earth and visa versa quite often.
- knodi123 2y ago
  yeah, but- dust and stray ions. nothing that could protect a bacteria from the extraordinary heat and energy of an explosion that launches it from the surface into space in a single titanic shove.

adrian_b 2y ago

If the bacteria were deep inside a rock ejected by an impact on a planet, which then falls as a meteorite on the other planet (as it is known to have happened for some meteorites fallen on Earth, which had been ejected from Mars or from Moon), then bacterial spores could survive, even if the external layers of the original rock are vaporized by the heat, if the rock had been big enough, so that the inner part would not have reached a high temperature. The same happens with the astronauts coming back to Earth, who survive despite the external shield being vaporized by the heat. If a body has low thermal conductivity and high thermal capacity, the inner part will maintain a low enough temperature, even when the outer part is above boiling temperature. On Earth, one can find bacteria in some rocks that are not completely compact, but which have pores or crevices, through which the water and gases needed by bacteria can pass. Such events would be unlikely, but not impossible. In the early Solar System, when big impacts were very frequent, there must have been many cases of rocks traveling between close planets, in all directions. After the planets had reached their current structure, meteorites coming from either Mars or Moon to Earth have remained frequent, due to the lack of a thick atmosphere on Mars and Moon, combined with their weaker gravity, but meteorites going from Earth to any of them have become extremely unlikely, because most bodies colliding with the Earth do not reach its surface, and for the few that reach the surface the probability that an ejected rock could exit Earth's atmosphere is even lower.

knodi123 2y ago
> and for the few that reach the surface the probability that an ejected rock could exit Earth's atmosphere is even lower. Ah, but the case I was replying to was about rocks making the trip back in the era when earth and mars both had enough atmosphere to support flowing liquid water.

pyinstallwoes 2y ago

Particles from Venus reach earth and visa versa quite often.

knodi123 2y ago
yeah, but- dust and stray ions. nothing that could protect a bacteria from the extraordinary heat and energy of an explosion that launches it from the surface into space in a single titanic shove.